JPS6254161B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a composite powder having iron as the outermost layer and a method for producing the same. In particular, the present invention relates to an iron-coated composite powder that can be usefully used in self-lubricating iron-based compacted powder sintered bodies such as friction materials and bearing materials, and a method for producing the same. Conventional technology and its problems Conventionally, in the production of self-lubricating iron-based compacted powder sintered bodies, solid lubricants such as graphite, molybdenum disulfide, boron nitride, etc. are mixed with iron powder; A method of pressure forming and sintering was attempted, but it was difficult to homogeneously disperse the solid lubricant in the iron powder, and the sintering properties of both were poor, making it impossible to obtain a high-strength sintered material. . Therefore, instead of mixing solid lubricant and iron powder, the use of iron-coated composite powder, which is solid lubricant powder coated with iron, was considered. However, it is extremely difficult to directly plate iron on solid lubricant powder, and although a direct coating method using thermal decomposition of iron pentacarbonyl has been reported, process control is difficult and costs are high. Further, JP-A-54-76768 discloses a technique in which the surface of metal sulfide particles is coated with a platinum group metal layer to activate the surface, and then coated with iron, copper, nickel, or cobalt. As a coating method for the platinum group metal layer, thermal decomposition of a platinum group compound containing a type of radical selected from NO, NO ₂ , NO ₃ and NOCl is said to be particularly preferred. Although it is possible to coat iron on platinum group metal coatings using this technique, it is not always possible to obtain a uniform coating with sufficient adhesion, as iron is more difficult to plate than copper or nickel. It was not completely guaranteed. When using the thermal decomposition method of noble metal salts, the surface obtained is in the form of fine powder. Therefore, it cannot be said to be ideal as a base surface to be plated with iron. In order to plate iron, which is difficult to plate, with good adhesion, it is ideal to use a smooth metallized surface as the base. Recently, there has been increasing interest in iron-based compacted powder sintered bodies containing molybdenum disulfide or boron nitride, and for this purpose, it is absolutely necessary to develop a composite powder in which they are coated with iron with good adhesion. OBJECTS OF THE INVENTION The purpose of the present invention is to establish a technology for producing iron-coated composite powder having a core of molybdenum disulfide or boron nitride using a general plating technique. Summary of the Invention It is extremely difficult to directly plate iron on molybdenum disulfide or boron nitride powder using common plating techniques. Therefore, the present inventors came up with the idea of interposing an intermediate metal layer and plating iron as the outermost layer thereon, and conducted repeated studies. As a result, (i) tin, nickel, and copper can be coated with good adhesion on molybdenum disulfide or boron nitride core powder activated with noble metal salts, and (ii) tin, nickel, and copper can be selected from the above. (iii) between the core powder and the intermediate layer and between the intermediate layer and the outermost layer; The adhesion was extremely high, and it was confirmed that a sintered material with high sintering strength could be obtained using the resulting composite powder. In this way, the present invention is the first in the world to produce iron having a structure of (molybdenum disulfide or boron nitride powder) - (intermediate coating layer of one or more of tin, nickel or copper) - (outermost iron layer). A coated composite powder is provided. As a method for suitably producing this composite powder, the present invention also includes activating the surface of molybdenum disulfide powder or boron nitride powder with a noble metal salt, and then adding at least one of tin, nickel, or copper to the surface of the molybdenum disulfide powder or boron nitride powder. a first step of coating the metal;
It is characterized by a second step of mixing the coated powder obtained in the first step with iron chloride powder and a powder containing one or more metals having a greater ionization tendency than iron, and then adding water or dilute hydrochloric acid. Provided is a method for producing iron-coated composite powder. DETAILED DESCRIPTION OF THE INVENTION In the present invention, molybdenum disulfide and boron nitride are used as the core coating powder. The particle size of the coating powder used in the present invention is suitably between -5 mesh and +400 mesh. If particles with a size larger than 5 meshes are used, the coating will be non-uniform, while if the particle size is smaller than 400 meshes, the problem of reduced fluidity and surface oxidation of the resulting iron-coated composite powder itself will occur. The method of activating the coated powder with a noble metal salt is carried out by treating the powder with an aqueous noble metal salt solution and then thermally decomposing the powder. Here, the precious metals include palladium, platinum, rhodium, gold, silver, and the like. Treatment with aqueous salt solutions includes immersion, mixing,
This refers to the process of adhering to coated powder by spraying, etc. This noble metal salt solution usually has a very low concentration, but depending on the desired thickness of the noble metal layer, a concentrated solution may be prepared or a layer coating process may be performed. After the noble metal salt treatment, the coated powder is heated to a required temperature to decompose and form the metal layer. The heating temperature is set to be higher than the decomposition temperature of the metal salt used, and when a high temperature is required for decomposition, heating is preferably carried out under a reducing atmosphere. When palladium is used as the noble metal, the thickness of the noble metal layer may be from several angstroms to several + angstroms, but it is not particularly limited to a certain value, and the lowest effective value is used mainly for economic reasons. In terms of quantity, it is 0.005W/ for coated powder.
W% or more, preferably 0.01W/W% or more,
This ratio depends on the surface shape and particle size distribution of the coated powder. After this, the intermediate layer is applied. The intermediate layer must be capable of forming a film with good adhesion to molybdenum disulfide powder and boron nitride powder, and at the same time provide a good plating surface to iron. Furthermore, it is also necessary that the boiling point be high. This is because if the boiling point is not high, it will volatilize during sintering, reducing the strength of the sintered body. From this point of view, the present invention uses one or more of tin, nickel and copper as the intermediate layer. The intermediate layer metal is plated by a known plating method such as a cementation method, an electroplating method, or a chemical plating method. The plating thickness should be 0.8 to 0.1 as long as it can provide a good plating surface for iron plating.
A thickness of μ is sufficient. After forming the intermediate layer, iron is applied as the outermost layer using cementation techniques using iron chloride powder.
The reason why the outermost layer is made of iron in the present invention is because, as stated at the beginning, the composite powder is intended to be used in an iron-based compacted powder sintered body. By sintering the composite powder after compacting, the outermost iron layer forms an iron matrix. Furthermore, when this composite powder is used together with iron powder, the presence of the outermost layer of iron improves dispersibility and familiarity, making it possible to increase the strength of the sintered body. In iron coating, the intermediate layer coating powder, iron chloride powder, and metal powder having a higher ionization tendency than iron, which is a reducing medium, are mixed. During this mixing, the reaction starts several seconds after mixing, but the reaction starts at the point when some white fume is generated due to the start of the reaction, that is, from 30 seconds to
After mixing for 2 minutes, unless water or dilute hydrochloric acid is added, the reaction will stop and solidification will occur. However, if water or dilute hydrochloric acid is added immediately after mixing, the reaction will not proceed, so care must be taken. The amount of water or dilute hydrochloric acid added at this time is 100ml per 100g of iron chloride powder used.
It is as follows. This is because if the amount is larger than that, it will affect the precipitation of iron. The reducing medium used here may be any metal that has a greater ionization tendency than iron, but calcium, magnesium, and aluminum are particularly preferred.
It may also be an alloy powder. Also, the form of iron used here must be iron chloride. Iron compounds such as iron sulfate, iron nitrate, and iron hydroxide do not cause the desired reaction related to the present invention. The temperature in the cementation process may be started from a solution at room temperature and allowed to rise due to the heat of reaction, but usually reaches 90 to 100°C. Effects of the Invention As described above, the present invention provides a composite powder coated with iron. The present invention enables the coating of iron with good adhesion on molybdenum disulfide and boron nitride powders, which has not been possible using conventional plating techniques, and the coating of tin, nickel or copper with good plating properties on precious metals. It is made possible by first forming it on powder activated by salt, and then coating the resulting smooth metallized surface with iron using cementation technology. This made it possible to obtain a sintered material based on this method. Furthermore, by making it possible to coat molybdenum disulfide with iron, the adhesion between iron and molybdenum disulfide is greatly improved compared to a sintered body of a mixed powder of molybdenum disulfide powder and iron powder. This made it possible to obtain a high-performance self-lubricating material. Examples of the present invention will be described below. Example Commercially available molybdenum disulfide powder (-150 mesh ~
50 ml of ammine palladium nitrate aqueous solution (containing 0.01 g of palladium) was added and mixed to 100 g of +325 mesh, and heated on a porcelain plate in the air at 300° C. for 60 minutes to form a thin palladium layer. This palladium-treated molybdenum disulfide powder was mixed with nickel chloride (NiCl ₂ 4H ₂ O) 42 g/, NH ₄ Cl 70 g/,
Lotusel salt 13g/, sodium hypophosphite 139g/
111.0 g of coated molybdenum disulfide powder was obtained. The amount of nickel plated was about 10%. Next, 740 g of iron chloride powder was added to 100 g of molybdenum disulfide powder treated with nickel, followed by 48 g of reducing aluminum powder (-400 mesh), followed by mixing and stirring. When some white fume was observed, about 500 ml of water was added and stirring was continued for about 60 seconds to uniformly precipitate iron onto the nickel-coated molybdenum disulfide powder by cementation. The resulting slurry was separated and washed with water, further subjected to anti-corrosion treatment with an aqueous solution having a benzotriazole concentration of 0.5 g/min, and dried under reduced pressure at 70 to 80°C to obtain a multilayer metal-coated molybdenum disulfide powder. The powder had a palladium thin layer thickness of 6 to 10 Å, a nickel layer thickness of about 0.3 μm, and an iron layer thickness of about 4 μm, showing extremely uniform thickness. The properties of the product were as follows.

[Table] Comparative Example Iron was coated using the cementation technique in the same manner as in the example except that the nickel plating layer was not interposed on the palladium thin layer. Although a certain degree of iron coating was obtained, the adhesion was not necessarily sufficient and the coverage was not uniform enough.
The sintered body produced using this iron-coated powder had a lower level of strength than the one using the powder of the example.

Claims (1)

[Scope of Claims] 1. An intermediate layer of one or more metals such as tin, nickel, or copper coated on the outer surface of molybdenum disulfide powder or boron nitride powder, and an outermost layer coated on the intermediate layer. Iron-coated composite powder with iron layer as 2. A first step of activating the surface of molybdenum disulfide powder or boron nitride powder with a noble metal salt, and then coating the surface with one or more of tin, nickel, or copper; and A second step of mixing the coated powder with iron chloride powder and a powder containing one or more metals having a higher ionization tendency than iron, and then adding water or dilute hydrochloric acid. Production method.